Trans fats, found in oils used to make cookies, crackers, microwave popcorn and to fry fast food, stay fresh longer than liquid fats. But the chemical process used to make them solid like butter also makes them clog arteries just like butter or lard does.

New York cities and counties were among the first to start banning them in restaurants and fast-food outlets.

“New York City was the first large metropolitan area in the United States to restrict trans fats in eateries, starting July 2007," the researchers wrote in their report in the Journal of the American Medical Association’s JAMA Cardiology.

Dr. Eric Brandt, of the Yale University School of Medicine, and colleagues checked medical records to see if it made any real difference. It did, they reported.

They compared counties where there were bans to counties where there were not.

“There was an additional 6.2 percent decline in hospital admissions for myocardial infarction (heart attack) and stroke among populations living in counties with vs without trans-fatty acid restrictions,” they wrote.

French fries made without trans fats taste just as good and aren't as likely to cause a heart attack or stroke. Shutterstock

“A nationwide trans fat ban is a win for the millions of people at risk for cardiovascular disease,” Brandt said in a statement.

The team did not measure deaths but lower rates of strokes and heart attacks have been shown in many studies to results in lower rates of deaths, as well.

The Food and Drug Administration has ruled that partially hydrogenated oils are no longer "generally recognized as safe" or GRAS. That means that after 2018, food manufacturers would have to ask the FDA for permission to use them in food products.

Trans fats are formed when liquid oils are chemically altered using a process called hydrogenization. This makes them similar to butter or lard. But the process almost makes these fats at least as unhealthy as, if not more unhealthy than, saturated fats.

The food industry and even health advocates at first thought they were better for health. It wasn't until the 1980s that medical research began to show clearly that they are not.

The debate confused the U.S. public, and many people still believe that butter is better for health than margarine. That may have been true of the old margarines made using hydrogenated oils, but it's less true now.

Butter does raise bad cholesterol, but margarines made using unsaturated fats and polyunsaturated fats do not.

“A nationwide trans fat ban is a win for the millions of people at risk for cardiovascular disease."

The FDA estimates that 80 percent of trans fats are already gone from U.S. foods.